Fuel economy

Scope

Fuel prices, and therefore fuel economy, are always at the forefront of a Fleet Manger’s mind.

The role of the driver in the fuel economy effort is an extremely important one. Personal efforts at high-efficiency driving can make a big difference. Some driving and handling techniques should be part of the basic skills package of a commercial motor vehicle (CMV) driver. These techniques have nothing to do with a specific piece of equipment, but they do have everything to do with common sense, good judgment, and intelligent decision-making. There can be as much as a 10% increase in the MPG rating if a vehicle is driven fuel-efficiently all the time.

Regulatory citations

• None

Key definitions

• Driving practices: Another way to cut fuel consumption is with common sense driving practices. These include efficient starting, smooth acceleration, and progressive shifting.
• Preventative maintenance: A solid preventive maintenance program helps a vehicle use fuel efficiently. Simple steps like making sure tires are properly inflated and the engine tuned on a regular basis can make a difference. Besides getting better mileage, routine maintenance reduces maintenance costs over the vehicle’s lifetime.
• Progressive shifting: This practice helps reduce wear, cuts noise, and saves fuel. In progressive shifting, you only accelerate enough to bring RPM up to the point where it’s possible to shift gears. Shifting before running the engine up to the governor saves fuel by not relying on the governor to limit power.
  
  There may be some situations when you need maximum power and need to run up to the governor, but in most cases a driver can upshift long before reaching the governor level. Shifting early should get a vehicle up to speed just as quickly. When a driver shifts early the governor doesn’t need to limit engine power while the driver goes through shifting.
  
  The overall goal of progressive shifting is smooth shifting to use as little fuel as possible. Progressive shifting works best for a driver who makes stops and shifts gears frequently. The advantage is less for over-the-road drivers.
• Smooth acceleration: After starting, select a gear that allows the vehicle to roll without slipping the clutch. Accelerate smoothly. Uneven action wastes fuel.
• Speed limits: You may be able to save fuel by traveling at slower speeds. Even though many states have speed limits over 65 mph on rural interstates, you may wish to consider setting governors/speed limiters at 65 mph or even a lower speed. Tests have proven that every mile per hour of additional speed over 55 mph costs an additional 2 to 2.2% in fuel consumption. Faster speed also increases air resistance, causing an engine to work harder at 65 mph than it would at 55 mph. The faster the vehicle travels the more horsepower is required to run the engine. The more horsepower expended, the greater fuel usage will be. Besides saving fuel, slowing down is safer and extends vehicle life.
• Starting the engine: When starting, take it easy. Long periods of cranking really waste fuel. If the engine doesn’t start after 30 seconds of cranking, stop and wait a couple of minutes before trying again. Don’t pump the accelerator and don’t rev the engine after it starts.
  Steady speed: Maintain steady speed. Braking unnecessarily causes loss of momentum. The only way to regain it is by accelerating, which burns more fuel.
• Trip planning: Besides saving time, good trip planning saves fuel. When selecting a route, consider fuel efficiency factors. Select a route with fewer stops and starts. Stop and go traffic or driving in small towns uses more fuel than driving a few miles to reach a controlled-access highway. The shortest route mileage-wise may not be the most efficient fuel-wise due to slowdowns for cross-traffic, driving through towns, hilly or mountainous terrain, etc. Snow and ice add road resistance, cutting into the engine’s efficiency. Poor visibility or slippery roads can cause the need to slow down and operate the engine at an inefficient speed.

Summary of requirements

Factors that determine fuel economy.

• Equipment specifications
• Vehicle maintenance
• Fuel quality
• Routing and load optimization
• Driving practices

Excessive idling. Engine idling can add significantly to overall fuel cost. On the average, between ½ and 1-½ gallons of fuel are burned each hour that an engine idles. Besides wasting fuel, excessive idling can foul fuel injectors, making the engine less efficient.

• Startup. In most cases there is no need to idle for a long time at the beginning of the day. Starting out slowly and smoothly allows lubricants to get circulating and is sufficient with newer tractors. When necessary, an engine should idle for no more than five minutes.
• Cool down. Cool down time at the end of the day should also be limited. After a hard run, cool down time should be limited to two or three minutes of low-RPM running under low engine-load conditions before turning off the engine. If the vehicle has traveled at a slow speed for at least 15 minutes (for example, on city streets), that time can replace the cool down time.
• Loading and unloading. Leaving an engine idle while loading and unloading a vehicle adds significantly to fuel costs. It takes less fuel to shut off and restart an engine than it does to leave it idling.

Besides the obvious waste of fuel, there are other valid reasons to avoid over-idling:

• Too much idling can clog fuel injection systems; because the engine isn’t hot enough for complete combustion, unburned fuel remains to cause harmful deposits.
• Idling is an inefficient warmup method since no movement of the vehicle is involved, meaning the transmission and tires stay cool.
• Another nasty aftermath of all that idling is about 41 million tons of exhaust emissions each year, and around 2000 tons of particulate matter thrown into the air. It also results in a greenhouse effect greater than from all refrigerants released by new cars.

Research and regulations. More and more states are passing measures to control CMV idling and long lists of metropolitan areas have made it clear they won’t tolerate excessive idling within their boundaries either. As one writer put it, “If various states and municipalities have their way, the word idle may soon mean In Danger with Law Enforcement!”

Impact. Argonne National Laboratory, located at the University of Chicago, does a great deal of work for the Department of Energy (DOE). It calculates that an average long-haul truck idles away as much as $4000 in profits each year. That’s a lot of money sent needlessly up those smokestacks! According to an estimate by the DOE Office of Heavy Vehicle Technologies, over three billion gallons of fuel are wasted each year at 0 mpg by all trucks and buses. Overnight idling by long-haul trucks wastes about 900 million gallons of fuel per year — that’s about 10% of all fuel consumed.